[RFC v3 2/2] media: staging: rkisp1: allow quantization conversion from userspace for isp source pad
Dafna Hirschfeld
dafna.hirschfeld at collabora.com
Mon Jun 29 08:08:39 EDT 2020
On 28.06.20 23:37, Laurent Pinchart wrote:
> Hi Tomasz,
>
> On Sun, Jun 28, 2020 at 11:33:30PM +0200, Tomasz Figa wrote:
>> On Sun, Jun 28, 2020 at 10:27 PM Laurent Pinchart wrote:
>>> On Sun, Jun 28, 2020 at 04:59:34PM +0200, Tomasz Figa wrote:
>>>> On Sun, Jun 28, 2020 at 3:15 PM Laurent Pinchart wrote:
>>>>> On Sun, Jun 28, 2020 at 03:10:41PM +0200, Tomasz Figa wrote:
>>>>>> On Fri, Jun 26, 2020 at 2:15 AM Helen Koike <helen.koike at collabora.com> wrote:
>>>>>>> On 6/18/20 4:25 PM, Tomasz Figa wrote:
>>>>>>>> On Thu, Jun 18, 2020 at 08:54:34PM +0200, Dafna Hirschfeld wrote:
>>>>>>>>> On 18.06.20 20:49, Tomasz Figa wrote:
>>>>>>>>>> On Thu, Jun 18, 2020 at 08:26:33PM +0200, Dafna Hirschfeld wrote:
>>>>>>>>>>> On 18.06.20 19:27, Tomasz Figa wrote:
>>>>>>>>>>>> On Wed, Jun 10, 2020 at 2:08 PM Tomasz Figa wrote:
>>>>>>>>>>>>> On Thu, Jun 4, 2020 at 9:11 PM Dafna Hirschfeld wrote:
>>>>>>>>>>>>>> On 04.06.20 19:54, Tomasz Figa wrote:
>>>>>>>>>>>>>>> On Thu, Apr 16, 2020 at 04:56:05PM +0200, Dafna Hirschfeld wrote:
>>>>>>>>>>>>>>>> The isp entity has a hardware support to force full range quantization
>>>>>>>>>>>>>>>> for YUV formats. Use the new API to indicate userspace that
>>>>>>>>>>>>>>>> quantization conversion is supported by adding the flag
>>>>>>>>>>>>>>>> V4L2_SUBDEV_MBUS_CODE_CSC_QUANTIZATION during media code enumeration.
>>>>>>>>>>>>>>>> Then uppon s_fmt on the video source pad, we assign the
>>>>>>>>>>>>>>>> quantization from userspace for YUV formats.
>>>>>>>>>>>>>>>> Also in the capture and resizer entities we retrieve the colorspace
>>>>>>>>>>>>>>>> from the isp entity.
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> Signed-off-by: Dafna Hirschfeld <dafna.hirschfeld at collabora.com>
>>>>>>>>>>>>>>>> ---
>>>>>>>>>>>>>>>> drivers/staging/media/rkisp1/rkisp1-capture.c | 28 ++++++-------
>>>>>>>>>>>>>>>> drivers/staging/media/rkisp1/rkisp1-common.h | 2 +
>>>>>>>>>>>>>>>> drivers/staging/media/rkisp1/rkisp1-isp.c | 39 +++++++++++++++++--
>>>>>>>>>>>>>>>> drivers/staging/media/rkisp1/rkisp1-resizer.c | 13 +++++++
>>>>>>>>>>>>>>>> 4 files changed, 65 insertions(+), 17 deletions(-)
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> diff --git a/drivers/staging/media/rkisp1/rkisp1-capture.c b/drivers/staging/media/rkisp1/rkisp1-capture.c
>>>>>>>>>>>>>>>> index fbf62399fe3d..aca0f93bc772 100644
>>>>>>>>>>>>>>>> --- a/drivers/staging/media/rkisp1/rkisp1-capture.c
>>>>>>>>>>>>>>>> +++ b/drivers/staging/media/rkisp1/rkisp1-capture.c
>>>>>>>>>>>>>>>> @@ -1066,14 +1066,13 @@ static void rkisp1_try_fmt(const struct rkisp1_capture *cap,
>>>>>>>>>>>>>>>> const struct v4l2_format_info **fmt_info)
>>>>>>>>>>>>>>>> {
>>>>>>>>>>>>>>>> const struct rkisp1_capture_config *config = cap->config;
>>>>>>>>>>>>>>>> - struct rkisp1_capture *other_cap =
>>>>>>>>>>>>>>>> - &cap->rkisp1->capture_devs[cap->id ^ 1];
>>>>>>>>>>>>>>>> const struct rkisp1_capture_fmt_cfg *fmt;
>>>>>>>>>>>>>>>> const struct v4l2_format_info *info;
>>>>>>>>>>>>>>>> const unsigned int max_widths[] = { RKISP1_RSZ_MP_SRC_MAX_WIDTH,
>>>>>>>>>>>>>>>> RKISP1_RSZ_SP_SRC_MAX_WIDTH };
>>>>>>>>>>>>>>>> const unsigned int max_heights[] = { RKISP1_RSZ_MP_SRC_MAX_HEIGHT,
>>>>>>>>>>>>>>>> RKISP1_RSZ_SP_SRC_MAX_HEIGHT};
>>>>>>>>>>>>>>>> + struct v4l2_subdev_format isp_sd_fmt;
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> fmt = rkisp1_find_fmt_cfg(cap, pixm->pixelformat);
>>>>>>>>>>>>>>>> if (!fmt) {
>>>>>>>>>>>>>>>> @@ -1081,24 +1080,27 @@ static void rkisp1_try_fmt(const struct rkisp1_capture *cap,
>>>>>>>>>>>>>>>> pixm->pixelformat = fmt->fourcc;
>>>>>>>>>>>>>>>> }
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> + rkisp1_get_isp_src_fmt(cap->rkisp1, &isp_sd_fmt);
>>>>>>>>>>>>>>>> + pixm->field = isp_sd_fmt.format.field;
>>>>>>>>>>>>>>>> + pixm->colorspace = isp_sd_fmt.format.colorspace;
>>>>>>>>>>>>>>>> + pixm->ycbcr_enc = isp_sd_fmt.format.ycbcr_enc;
>>>>>>>>>>>>>>>> + pixm->xfer_func = isp_sd_fmt.format.xfer_func;
>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>> + /*
>>>>>>>>>>>>>>>> + * isp has a feature to set full range quantization for yuv formats.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> How about "select between limited and full range for YUV formats"?
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> + * so we need to get the format from the isp.
>>>>>>>>>>>>>>>> + */
>>>>>>>>>>>>>>>> + pixm->quantization = isp_sd_fmt.format.quantization;
>>>>>>>>>>>>>>>> + if (!v4l2_is_format_yuv(cap->pix.info))
>>>>>>>>>>>>>>>> + pixm->quantization = V4L2_QUANTIZATION_FULL_RANGE;
>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>> pixm->width = clamp_t(u32, pixm->width,
>>>>>>>>>>>>>>>> RKISP1_RSZ_SRC_MIN_WIDTH, max_widths[cap->id]);
>>>>>>>>>>>>>>>> pixm->height = clamp_t(u32, pixm->height,
>>>>>>>>>>>>>>>> RKISP1_RSZ_SRC_MIN_HEIGHT, max_heights[cap->id]);
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> - pixm->field = V4L2_FIELD_NONE;
>>>>>>>>>>>>>>>> - pixm->colorspace = V4L2_COLORSPACE_DEFAULT;
>>>>>>>>>>>>>>>> - pixm->ycbcr_enc = V4L2_YCBCR_ENC_DEFAULT;
>>>>>>>>>>>>>>>> -
>>>>>>>>>>>>>>>> info = rkisp1_fill_pixfmt(pixm, cap->id);
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> - /* can not change quantization when stream-on */
>>>>>>>>>>>>>>>> - if (other_cap->is_streaming)
>>>>>>>>>>>>>>>> - pixm->quantization = other_cap->pix.fmt.quantization;
>>>>>>>>>>>>>>>> - /* output full range by default, take effect in params */
>>>>>>>>>>>>>>>> - else if (!pixm->quantization ||
>>>>>>>>>>>>>>>> - pixm->quantization > V4L2_QUANTIZATION_LIM_RANGE)
>>>>>>>>>>>>>>>> - pixm->quantization = V4L2_QUANTIZATION_FULL_RANGE;
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> if (fmt_cfg)
>>>>>>>>>>>>>>>> *fmt_cfg = fmt;
>>>>>>>>>>>>>>>> diff --git a/drivers/staging/media/rkisp1/rkisp1-common.h b/drivers/staging/media/rkisp1/rkisp1-common.h
>>>>>>>>>>>>>>>> index 2d7b7e078636..7a5576fa14c9 100644
>>>>>>>>>>>>>>>> --- a/drivers/staging/media/rkisp1/rkisp1-common.h
>>>>>>>>>>>>>>>> +++ b/drivers/staging/media/rkisp1/rkisp1-common.h
>>>>>>>>>>>>>>>> @@ -300,6 +300,8 @@ int rkisp1_isp_register(struct rkisp1_device *rkisp1,
>>>>>>>>>>>>>>>> struct v4l2_device *v4l2_dev);
>>>>>>>>>>>>>>>> void rkisp1_isp_unregister(struct rkisp1_device *rkisp1);
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> +int rkisp1_get_isp_src_fmt(struct rkisp1_device *rkisp1,
>>>>>>>>>>>>>>>> + struct v4l2_subdev_format *sd_fmt);
>>>>>>>>>>>>>>>> const struct rkisp1_isp_mbus_info *rkisp1_isp_mbus_info_get(u32 mbus_code);
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> irqreturn_t rkisp1_isp_isr(struct rkisp1_device *rkisp1);
>>>>>>>>>>>>>>>> diff --git a/drivers/staging/media/rkisp1/rkisp1-isp.c b/drivers/staging/media/rkisp1/rkisp1-isp.c
>>>>>>>>>>>>>>>> index dee8e96f3900..6fdf5ed0b6b1 100644
>>>>>>>>>>>>>>>> --- a/drivers/staging/media/rkisp1/rkisp1-isp.c
>>>>>>>>>>>>>>>> +++ b/drivers/staging/media/rkisp1/rkisp1-isp.c
>>>>>>>>>>>>>>>> @@ -613,6 +613,10 @@ static int rkisp1_isp_enum_mbus_code(struct v4l2_subdev *sd,
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> if (code->index == pos - 1) {
>>>>>>>>>>>>>>>> code->code = fmt->mbus_code;
>>>>>>>>>>>>>>>> + if (fmt->pixel_enc == V4L2_PIXEL_ENC_YUV &&
>>>>>>>>>>>>>>>> + dir == RKISP1_DIR_SRC)
>>>>>>>>>>>>>>>> + code->flags =
>>>>>>>>>>>>>>>> + V4L2_SUBDEV_MBUS_CODE_CSC_QUANTIZATION;
>>>>>>>>>>>>>>>> return 0;
>>>>>>>>>>>>>>>> }
>>>>>>>>>>>>>>>> }
>>>>>>>>>>>>>>>> @@ -639,12 +643,21 @@ static int rkisp1_isp_init_config(struct v4l2_subdev *sd,
>>>>>>>>>>>>>>>> sink_crop->height = RKISP1_DEFAULT_HEIGHT;
>>>>>>>>>>>>>>>> sink_crop->left = 0;
>>>>>>>>>>>>>>>> sink_crop->top = 0;
>>>>>>>>>>>>>>>> + sink_fmt->colorspace = V4L2_COLORSPACE_SRGB;
>>>>>>>>>>>>>>>> + sink_fmt->ycbcr_enc = V4L2_MAP_YCBCR_ENC_DEFAULT(sink_fmt->colorspace);
>>>>>>>>>>>>>>>> + sink_fmt->xfer_func = V4L2_MAP_XFER_FUNC_DEFAULT(sink_fmt->colorspace);
>>>>>>>>>>>>>>>> + sink_fmt->quantization = V4L2_QUANTIZATION_FULL_RANGE;
>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> src_fmt = v4l2_subdev_get_try_format(sd, cfg,
>>>>>>>>>>>>>>>> RKISP1_ISP_PAD_SOURCE_VIDEO);
>>>>>>>>>>>>>>>> *src_fmt = *sink_fmt;
>>>>>>>>>>>>>>>> src_fmt->code = RKISP1_DEF_SRC_PAD_FMT;
>>>>>>>>>>>>>>>> - src_fmt->quantization = V4L2_QUANTIZATION_FULL_RANGE;
>>>>>>>>>>>>>>>> + src_fmt->colorspace = V4L2_COLORSPACE_SRGB;
>>>>>>>>>>>>>>>> + src_fmt->ycbcr_enc = V4L2_MAP_YCBCR_ENC_DEFAULT(src_fmt->colorspace);
>>>>>>>>>>>>>>>> + src_fmt->xfer_func = V4L2_MAP_XFER_FUNC_DEFAULT(src_fmt->colorspace);
>>>>>>>>>>>>>>>> + src_fmt->quantization = V4L2_QUANTIZATION_LIM_RANGE;
>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> src_crop = v4l2_subdev_get_try_crop(sd, cfg,
>>>>>>>>>>>>>>>> RKISP1_ISP_PAD_SOURCE_VIDEO);
>>>>>>>>>>>>>>>> @@ -687,10 +700,17 @@ static void rkisp1_isp_set_src_fmt(struct rkisp1_isp *isp,
>>>>>>>>>>>>>>>> isp->src_fmt = mbus_info;
>>>>>>>>>>>>>>>> src_fmt->width = src_crop->width;
>>>>>>>>>>>>>>>> src_fmt->height = src_crop->height;
>>>>>>>>>>>>>>>> - src_fmt->quantization = format->quantization;
>>>>>>>>>>>>>>>> - /* full range by default */
>>>>>>>>>>>>>>>> - if (!src_fmt->quantization)
>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>> + src_fmt->colorspace = V4L2_COLORSPACE_SRGB;
>>>>>>>>>>>>>>>> + src_fmt->ycbcr_enc = V4L2_MAP_YCBCR_ENC_DEFAULT(src_fmt->colorspace);
>>>>>>>>>>>>>>>> + src_fmt->xfer_func = V4L2_MAP_XFER_FUNC_DEFAULT(src_fmt->colorspace);
>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>> + if (mbus_info->pixel_enc == V4L2_PIXEL_ENC_BAYER)
>>>>>>>>>>>>>>>> src_fmt->quantization = V4L2_QUANTIZATION_FULL_RANGE;
>>>>>>>>>>>>>>>> + else if (format->quantization == V4L2_QUANTIZATION_DEFAULT)
>>>>>>>>>>>>>>>> + src_fmt->quantization = V4L2_QUANTIZATION_LIM_RANGE;
>>>>>>>>>>>>>>>> + else
>>>>>>>>>>>>>>>> + src_fmt->quantization = format->quantization;
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> *format = *src_fmt;
>>>>>>>>>>>>>>>> }
>>>>>>>>>>>>>>>> @@ -1068,6 +1088,17 @@ int rkisp1_isp_register(struct rkisp1_device *rkisp1,
>>>>>>>>>>>>>>>> return ret;
>>>>>>>>>>>>>>>> }
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> +int rkisp1_get_isp_src_fmt(struct rkisp1_device *rkisp1,
>>>>>>>>>>>>>>>> + struct v4l2_subdev_format *sd_fmt)
>>>>>>>>>>>>>>>> +{
>>>>>>>>>>>>>>>> + struct rkisp1_isp *isp = &rkisp1->isp;
>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>> + sd_fmt->which = V4L2_SUBDEV_FORMAT_ACTIVE;
>>>>>>>>>>>>>>>> + sd_fmt->pad = RKISP1_ISP_PAD_SOURCE_VIDEO;
>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>> + return v4l2_subdev_call(&isp->sd, pad, get_fmt, NULL, sd_fmt);
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> Do we need to get through the external API to access data that is
>>>>>>>>>>>>>>> driver-internal anyway?
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> +}
>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>> void rkisp1_isp_unregister(struct rkisp1_device *rkisp1)
>>>>>>>>>>>>>>>> {
>>>>>>>>>>>>>>>> struct v4l2_subdev *sd = &rkisp1->isp.sd;
>>>>>>>>>>>>>>>> diff --git a/drivers/staging/media/rkisp1/rkisp1-resizer.c b/drivers/staging/media/rkisp1/rkisp1-resizer.c
>>>>>>>>>>>>>>>> index 7b6b7ddd4169..8705b133de68 100644
>>>>>>>>>>>>>>>> --- a/drivers/staging/media/rkisp1/rkisp1-resizer.c
>>>>>>>>>>>>>>>> +++ b/drivers/staging/media/rkisp1/rkisp1-resizer.c
>>>>>>>>>>>>>>>> @@ -525,6 +525,7 @@ static void rkisp1_rsz_set_sink_fmt(struct rkisp1_resizer *rsz,
>>>>>>>>>>>>>>>> const struct rkisp1_isp_mbus_info *mbus_info;
>>>>>>>>>>>>>>>> struct v4l2_mbus_framefmt *sink_fmt, *src_fmt;
>>>>>>>>>>>>>>>> struct v4l2_rect *sink_crop;
>>>>>>>>>>>>>>>> + struct v4l2_subdev_format isp_sd_fmt;
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> sink_fmt = rkisp1_rsz_get_pad_fmt(rsz, cfg, RKISP1_RSZ_PAD_SINK, which);
>>>>>>>>>>>>>>>> src_fmt = rkisp1_rsz_get_pad_fmt(rsz, cfg, RKISP1_RSZ_PAD_SRC, which);
>>>>>>>>>>>>>>>> @@ -539,8 +540,20 @@ static void rkisp1_rsz_set_sink_fmt(struct rkisp1_resizer *rsz,
>>>>>>>>>>>>>>>> if (which == V4L2_SUBDEV_FORMAT_ACTIVE)
>>>>>>>>>>>>>>>> rsz->pixel_enc = mbus_info->pixel_enc;
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> + rkisp1_get_isp_src_fmt(rsz->rkisp1, &isp_sd_fmt);
>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> Is this necessary? My understanding was that in the subdev model, it was
>>>>>>>>>>>>>>> the userspace responsibility to propagate any configuration changes through
>>>>>>>>>>>>>>> the graph.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> Also, doing this only here wouldn't fully maintain the
>>>>>>>>>>>>>>> consistency of the state. For example, if one sets the ISP subdev format
>>>>>>>>>>>>>>> first, then the resizer subdev and then the ISP subdev again, wouldn't the
>>>>>>>>>>>>>>> resizer subdev end up with a wrong format?
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> yes, this is indeed a bug, I am preparing v4 now.
>>>>>>>>>>>>>> What I thought to do is adding quantization conversion
>>>>>>>>>>>>>> support also on ther resizer and capture entities.
>>>>>>>>>>>>>> Then in the 'link_validation' callbacks, there
>>>>>>>>>>>>>> is a validation that the quantization fields matches.
>>>>>>>>>>>>>
>>>>>>>>>>>>> My understanding is that, if we have the following topology
>>>>>>>>>>>>>
>>>>>>>>>>>>> [ ISP ] -> [ Resizer ] -> [ Video node ]
>>>>>>>>>>>>>
>>>>>>>>>>>>> then the ISP source pad would have the csc capability, while resizer
>>>>>>>>>>>>> and video node would just accept whatever is configured on their sink
>>>>>>>>>>>>> pads (no need for csc capability for that) and propagate that to their
>>>>>>>>>>>>> outputs, i.e. resizer source pad and video node CAPTURE format.
>>>>>>>>>>>>>
>>>>>>>>>>>>> Is this what you were going to implement?
>>>>>>>>>>> Hi, I sent a v4 where the CSC capability is set on the reiszer and capture as well.
>>>>>>>>>>> I can send a v5 implementing it the way you suggest. Currently the doc says that the colorspace fields
>>>>>>>>>>> must be set by the driver for capture streams. This implies that userspace can set it
>>>>>>>>>>> only if the CSC is supported.
>>>>>>>>>>
>>>>>>>>>> Why would the userspace have to set it for the capture stream on the
>>>>>>>>>> resizer and video nodes? Couldn't the userspace set it to DEFAULT and
>>>>>>>>>> then the driver override to whatever it received on the corresponding
>>>>>>>>>> sink?
>>>>>>>
>>>>>>> According to the documentation [1]:
>>>>>>>
>>>>>>> "the default quantization encoding as defined by the colorspace"
>>>>>>>
>>>>>>> Then, for instance, the default for V4L2_COLORSPACE_SRGB is limited range [2].
>>>>>>>
>>>>>>> Unless we change the definition of DEFAULT to let it accept whatever it receives on the corresponding sink.
>>>>>>>
>>>>>>> Then the way I understand is:
>>>>>>>
>>>>>>> [sensor]->[isp]->[resizer]->[capture]
>>>>>>>
>>>>>>> Userspace should set quantization on:
>>>>>>> * sensor source pad
>>>>>>> * isp sink pad
>>>>>>> * resizer sink pad
>>>>>>> * capture node
>>>>>>>
>>>>>>> The remaining source pads would get values propagated from their sink pads.
>>>>>>>
>>>>>>> [1] https://linuxtv.org/downloads/v4l-dvb-apis-new/userspace-api/v4l/colorspaces-defs.html#c.v4l2_quantization
>>>>>>> [2] https://linuxtv.org/downloads/v4l-dvb-apis-new/userspace-api/v4l/colorspaces-details.html#col-srgb
>>>>>>
>>>>>> After discussing this offline, we concluded that:
>>>>>> - only the source pad of the ISP entity should expose the CSC capability,
>>>>>> - the CAPTURE video node should expose only the formats/color spaces
>>>>>> compatible with the current setting of the resizer source,
>>>>>> - consistency between the resizer source format and CAPTURE format
>>>>>> should be implicitly maintained by the driver.
>>>>>
>>>>> Do you mean it should be validated at streamon time ?
>>>>
>>>> Nope. Any V4L2 state must be kept valid all the time, as mandated by
>>>> the general V4L2 principles. Wrong configuration of the video node
>>>> must not be a reason for STREAMON failing.
>>>
>>> That's a wrong interpretation of V4L2. On a video-node-centric device (a
>>> device that doesn't use the subdev userspace API for configuration) this
>>> is correct. In a MC-centric device, the video node and its connected
>>> subdev are configured separately.
>>
>> I don't see this documented anywhere in the specification, maybe
>> except a mention of EPIPE or ENOLINK being returned from STREAMON, but
>> they explicitly refer to pipeline configuration and not a conflict
>> between V4L2 and MC state.
>
> We're suffering from a lack of documentation in this area :-( Niklas has
> authored
>
> commit f645e6256bd1b12523b759fcc610861fb21c24c7
> Author: Niklas Söderlund <niklas.soderlund+renesas at ragnatech.se>
> Date: Tue Apr 21 15:57:38 2020 +0200
>
> media: v4l2-dev/ioctl: Add V4L2_CAP_IO_MC
>
> which is a first step, now we need to document the behaviour of all
> ioctls properly when the MC and !MC cases differ.
>
>> The behavior as you're suggesting would be at least confusing for the
>> userspace, because it breaks one of the core principles of V4L2 and
>> also there is even no facility to allow the userspace handle this kind
>> of behavior, e.g. how to know which memory formats are supported for
>> given mbus formats of the related sink.
>
> commit e5b6b07a1b45dd9d19bec1fa1d60750b0fcf2fb0
> Author: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> Date: Fri Apr 24 15:43:31 2020 +0200
>
> media: v4l2: Extend VIDIOC_ENUM_FMT to support MC-centric devices
Hi,
What if the video device entity wants to support V4L2_CAP_IO_MC and has two
pads registered to the media controller?
It seems to be undefined in the documentation.
Thanks,
Dafna
>
> Been missing for a long time... I realized that when I started using the
> API in a real userspace implementation instead of just writing test
> tools or very device-specific code that could hardcode all this
> knowledge.
>
>>>>> In MC-based
>>>>> drivers, entities are isolated from each other from a configuration
>>>>> point of view, and the validity of the configuration across the whole
>>>>> pipeline is checked at streamon time. I don't think CSC parameters
>>>>> should be treated differently than formats in this regard.
>>>>
>>>> Indeed, the ISP entity and the resizer entity are isolated from each
>>>> other and they need to be validated separately. However, the resizer
>>>> entity is not isolated from the video node, as there is no
>>>> configuration exposed for the video node in the MC API. If MC exposed
>>>> an explicit format control for the video interface sink pad, then the
>>>> resizer would have to be validated separately indeed, but still that
>>>> video interface sink pad would be tied to the rest of the
>>>> configuration of the video node (e.g. the CAPTURE format).
>>>>
>>>>>> Below is the rationale for that:
>>>>>> - In the MC model, the video node represents the DMA alone (and thus
>>>>>> the reason to have the resizer entities at all) and since the
>>>>>> colorspace is not a property of the DMA, it doesn't belong there.
>>>>>> - Even if we put that aside, both MP and SP can only output the same
>>>>>> colorspace, which would create a dependency between the configuration
>>>>>> of the two video nodes, which is not something well defined by V4L2.
>>>>>> - A video interface in the MC API doesn't expose control over its
>>>>>> input format, which means that the relation between the other side of
>>>>>> the link (resizer source) and the video node is implicit and needs to
>>>>>> be handled internally in the driver.
>>>>>> - V4L2, as opposed to MC, requires that the current state is always
>>>>>> consistent and valid. In this case it means that an ioctl on the video
>>>>>> node must not be able to alter the state in a way that would make it
>>>>>> inconsistent with the state of the matching resizer source.
>
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